feat: only highlight dates at which there exist certain diary

[allenfantasy]

Target Problem

By now, all dates between startDate and endDate in the Pikaday calendar could be clicked, which would guide users to a 404 not found page when there's no diary at the selected date.

Solution

use disableDayFn of Pikaday to disable all invalid dates (i.e: there's no diary at that day).

Screenshot